Cold-cathode fluorescent lamps (CCFL) have been traditionally used as light sources for backlight apparatuses of liquid crystal display apparatuses, but the number of backlight apparatuses using light-emitting diodes (LEDs) as light sources has recently also increased. Since an LED is a spot light source, when LEDs are used as the light sources of a backlight apparatus, the occurrence of brightness unevenness and color unevenness of the light emitted from the backlight apparatus needs to be suppressed by devising the arrangement of LEDs, a light diffusion structure, and a light reflection structure. In particular, in a backlight apparatus using LEDs of a plurality of colors, such as red color, green color, and blue color, brightness unevenness and color unevenness in the form of a stripe or grid pattern occur easier than in the backlight apparatuses using white-color LEDs. Therefore, the arrangement of LEDs, light diffusion structure, and light reflection structure need to be devised.
For example, Patent Literatures 1 to 3 disclose techniques for reducing color unevenness in a backlight apparatus (light source apparatus) using LEDs of three colors: red, green, and blue. Thus, Patent Literatures 1 to 3 disclose light source apparatuses having a plurality of light-emitting clusters.
In the light source apparatus disclosed in Patent Literature 1, light-emitting clusters of a plurality of types are used. In the light-emitting clusters disclosed in Patent Literature 1, the three LEDs have triangular arrangements, and the arrangements of red LEDs differ among the light-emitting clusters of a plurality of types. In the light source apparatus disclosed in Patent Literature 1, the types of the light-emitting clusters which are to be arranged are changed according to the arrangement positions of the light-emitting clusters.
In the light source apparatus disclosed in Patent Literature 2, light-emitting clusters are used which have a plurality of light-emitting elements that differ in color (emission color; the color of light emitted from a light-emitting element) from each other. With respect to at least one color, the light-emitting cluster disclosed in Patent Literature 2 has a plurality of light-emitting elements of this color. Further, in the light-emitting cluster disclosed in Patent Literature 2, the light-emitting elements are arranged such that the central positions of the light-emitting element of each color substantially match.
In the light source apparatus disclosed in Patent Literature 3, light-emitting clusters are used that have N spot light sources that differ in color. Further, in the light source apparatus disclosed in Patent Literature 3, each light-emitting cluster is arranged by being rotated clockwise or counterclockwise through a predetermined angle with respect to a light-emitting cluster adjacent to this light-emitting cluster.
Further, a technique is known by which the emission brightness of LEDs is individually changed by using the fact that LEDs are spot light sources, thereby changing partially the luminance of the backlight apparatus and increasing the contrast of the displayed image. Such control of emission brightness is typically called local dimming control. The local dimming control involves the processing of analyzing a brightness value of an image signal with respect to each of a plurality of divided regions constituting the screen region, and controlling the emission brightness of the corresponding light source on the basis of the analysis results of the brightness value. As a result, the contrast of the displayed image is increased. Further, by using light sources of a plurality of colors as the light sources corresponding to the divided regions, it is possible to change not only the mission brightness of the backlight apparatus but also the emission color for each divided region. More specifically, by changing the emission brightness ratio of light sources of a plurality of colors, it is possible to change the emission color of the backlight apparatus. By controlling the emission color of the backlight apparatus for each divided region, it is possible to expand the color gamut of the displayed image.
For example, Patent Literature 4 discloses the technique for reducing color unevenness in a light source apparatus that can be controlled by local dimming. More specifically, Patent Literature 4 discloses the technique for reducing color unevenness generated at the outer edges of light-emitting clusters. With the technique disclosed in Patent Literature 4, each of a plurality of light source units (light-emitting clusters) corresponding to a plurality of divided regions is constituted by a plurality of red LEDs, a plurality of green LEDs, and a plurality of blue LEDs. The LEDs are arranged such that the following condition is fulfilled for each light source unit.
Condition: the centroid of the brightness profile based on a plurality of red LEDs, the centroid of the brightness profile based on a plurality of green LEDs, and the centroid of the brightness profile based on a plurality of blue LEDs substantially match the centroid of the light source unit.